FIG. 23 shows a typical arrangement of a conventional image sensing system, and the operation of the conventional image sensing system will be briefly explained below with reference to FIG. 23. In this image sensing system, an object image is formed on an image sensing element 1 by an image sensing optical system 8, which has a focal length adjustment optical system L1 for adjusting the image sensing field angle, a correction optical system L2 for making correction corresponding to the movement of the optical system L1, a shift optical system L3 for camera-shake correction, an iris mechanism (Iris) for adjusting the amount of incoming light, and a focal point position adjustment optical system L4 for making focus adjustment. The image sensing element 1 photoelectrically converts the object image into an electrical signal, and a signal processor 3 processes the electrical signal to obtain a color video signal. The color video signal is output, and its luminance information is mainly supplied to an exposure control (AE) unit 4 and focus adjustment (AF) unit 2, thus generating respective control signals (see Japanese Patent Laid-Open Nos. 3-159377 and 8-190113).
The AE unit 4 controls the accumulation time (so-called shutter speed) of the image sensing element 1 for each frame, and the iris mechanism Iris, and the AF unit 2 controls the focal point position adjustment optical system L4.
A vibration sensor 7 comprises an acceleration sensor and the like, and detects any camera shake. A shift optical system driving (AS/IS) unit 6 reduces blur of an object image caused by camera shake by driving the shift optical system L3 using the detection output of the vibration sensor 7.
A field angle adjustment (zoom) unit 5 receives an operation instruction signal for adjusting the image sensing field angle in accordance with a user's request, reads out a digital cam curve from a memory (not shown), and controls the focal length adjustment optical system L1, correction optical system L2, and focal point position adjustment optical system L4 in cooperation with each other.
As described above, in recent years, along with a rapid size reduction of the image sensing system, a multi-function, high-performance, compact image sensing system can be realized. For example, Japanese Patent Laid-Open No. 3-159377 discloses contents associated with an electric tilt & shift control mechanism and multi-point AF evaluation. However, the image sensing element requires very high attachment precision.
For example, as shown in FIG. 24, an angle θ the optical axis of the image sensing optical system 8 makes with the image sensing element 1 often tilts from the vertical or horizontal position due to poor manufacturing precision of parts, attachment errors in the manufacturing process, and the like. In such case, as the system size becomes smaller, it becomes harder to make the angle θ fall within an allowable range, and it becomes difficult to adjust the angle at high precision that matches the current size reduction requirement.
Furthermore, as the image sensing element is down-sized, the focal length of the image sensing optical system becomes shorter, and the depth of field tends to become deeper. As a result, it becomes difficult to use a photographing technique that controls the depth of field (e.g., a shallow depth of field is set to make the background out of focus).